Antagonism of the cannabinoid CB-1 receptor protects rat liver against ischaemia-reperfusion injury complicated by endotoxaemia.

BACKGROUND/AIM: Endotoxaemia can complicate hepatic ischaemia-reperfusion (IR) injury. Endocannabinoids appear to modulate the haemodynamic alterations and cytokine response induced by lipopolysaccharide (LPS). Thus, we aimed to determine the effect of the endocannabinoid CB1-receptor antagonist Rimonabant in a model of hepatic IR injury complicated by endotoxaemia. METHODS: Sprague-Dawley rats pre-treated with Rimonabant 3 or 10 mg/kg or vehicle underwent partial hepatic IR and lipopolysaccharide (LPS) injection at reperfusion. Liver injury was evaluated by serum alanine aminotransferase (ALT) and necrotic-cell count. The inflammatory response was investigated by assessing hepatic neutrophil infiltration, tumour necrosis factor alpha (TNFalpha), interferon gamma (IFNgamma), interleukin 6 (IL6), and suppressor of cytokine signalling (SOCS) 1 and SOCS3 gene expression by real-time polymerase chain reaction (RT-PCR). Systolic blood pressure and hepatic blood flow were measured as haemodynamic parameters. Finally, lipid peroxidation, glutathione status, and immunoreactive CB1 receptor expression in the liver were also determined. RESULTS: Liver injury and neutrophil infiltration occurring in the late-phase of LPS-enhanced IR were significantly reduced by CB1-receptor antagonism. Rimonabant-treated rats showed significantly higher gene expression of IFNgamma, IL6, SOCS1 and SOCS3 in "early" reperfusion, while that of TNFalpha was reduced. These findings were associated with increased STAT3 phosphorylation. Furthermore, CB1-receptor antagonism significantly improved the oxidative injury and haemodynamic alterations occurring during reperfusion in untreated rats. Finally, CB1-receptor immunoreactivity was upregulated early after reperfusion. CONCLUSIONS: This study demonstrates that CB1-receptor antagonism protects the liver against LPS-enhanced IR injury by interfering with the inflammatory response that causes the late, neutrophil-dependent phase of reperfusion injury, although the prevention of the transient endotoxin-related hypotension occurring early during reperfusion may be also involved.

Oxidative injury in rat fatty liver exposed to ischemia-reperfusion is modulated by nutritional status.

BACKGROUND AND AIMS: Oxidative stress contributes to ischemia-reperfusion injury in fatty livers. This study aimed to determine whether glycogen depletion influences this oxidative injury and whether the administration of glucose can be protective. METHODS: Rats with choline deficiency-induced fatty liver underwent hepatic ischemia-reperfusion. Experimental groups: (1) fed rats; (2) 18 h fasted rats; (3) 18 h fasted rats supplemented with glucose prior to surgery. The thiobarbituric acid-reactive substances, protein carbonyls and total glutathione concentrations were measured in liver tissue and isolated mitochondria as parameters of oxidative stress before and after ischemia and during reperfusion. The mitochondrial F1-ATPase content and the serum alanine transaminase were also determined. RESULTS: With respect to fed rats, fasted rats exhibited an increased oxidative injury in both liver tissue and isolated mitochondria throughout the experiment with the only exception of thiobarbituric acid-reactive substances, which were not affected by the nutritional status in liver tissue. Fasted rats showed a significantly lower F1-ATPase content and higher alanine transaminase levels. Glucose supplementation significantly reduced the fasting-associated exacerbation of oxidative stress and liver injury and the F1-ATPase exhaustion. CONCLUSIONS: These data indicate that the pre-existing hepatic glycogen content modulates the oxidative damage in rat fatty livers exposed to ischemia-reperfusion injury and that the energetic substrate supplementation may represent a clinically feasible protective strategy.

Experimental observations and clinical implications of fasting and diet supplementation in fatty livers.

Fatty accumulation per se does not appear to affect liver function; however, interest has recently renewed to fatty liver because of the clinical relevance of non alcoholic steato-hepatitis (NASH) and for the increased risk of post-transplant failure in grafted livers with steatosis. Clinical and experimental studies have doubtless demonstrated that oxidative stress ensues in steatotic livers. Mitochondria represent the preferential target of the oxidative injury associated to fatty degeneration and show reduced content of glutathione, higher levels of oxidative products and damages to enzymes involved in the process of ATP synthesis, which become more evident under stressing conditions. Although obese patients with fatty liver are advantaged by weight loss, clinical and experimental observations suggest that fatty livers poorly tolerate excessive food deprivation. These observations represent the rationale for treatment strategies based on the supplementation of antioxidants and energetic substrates rather than solely a diet restriction. This review focuses on data emerging from a series of investigations performed in rats with fatty livers induced by a choline-deficient diet, which resembles human steatosis due to an excessive intake of carbohydrates, and aims to give the cue for the development of therapeutic options able to preserve hepatic function after transplantation of steatotic organs.

Ischemia-reperfusion injury in rat fatty liver: role of nutritional status.

Fatty livers are more sensitive to the deleterious effects of ischemia-reperfusion than normal livers. Nutritional status greatly modulates this injury in normal livers, but its role in the specific setting of fatty liver is unknown. This study aimed to determine the effect of nutritional status on warm ischemia-reperfusion injury in rat fatty livers. Fed and fasted rats with normal or fatty liver induced by a choline deficient diet underwent 1 hour of lobar ischemia and reperfusion. Rat survival was determined for 7 days. Serum transaminases, liver histology and cell ultrastructure were assessed before and after ischemia, and at 30 minutes, 2 hours, 8 hours, and 24 hours after reperfusion. Survival was also determined in fatty fasted rats supplemented with glucose before surgery. The preischemic hepatic glycogen was measured in all groups. Whereas survival was similar in fasted and fed rats with normal liver (90% vs. 100%), fasting dramatically reduced survival in rats with fatty liver (14% vs. 64%, P <.01). Accordingly, fasting and fatty degeneration had a synergistic effect in exacerbating liver injury. Mitochondrial damage was a predominant feature of ultrastructural hepatocyte injury in fasted fatty livers. Glucose supplementation partially prevented the fasting-induced depletion of glycogen and improved the 7-day rat survival to 45%. These data indicate that rat fatty livers exposed to normothermic ischemia-reperfusion injury are much more sensitive to fasting than histologically normal livers. Because glucose supplementation improves both the hepatic glycogen stores and the rat survival, a nutritional repletion procedure may be part of a treatment strategy aimed to prevent ischemia-reperfusion injury in fatty livers.